Magnetic tape cartridge

ABSTRACT

Disclosed herein is a magnetic tape cartridge including a reel-rotation restraining member which restricts rotation of a reel when not used and allows the rotation of the reel when used. The reel-rotation restraining member has a restraining member, an urging member, and an unlocking member. The restraining member has a restraining gear which meshes with a locking tooth portion, and the restraining member is supported by a support portion of the cartridge case. In the magnetic tape cartridge, the following relationship is met:  
       b ≦(2× a×c )/ d    
     where “a” represents the length of engagement between the restraining member in an unlocked state and the support portion, “b” represents the clearance between the restraining member and the support portion, “c” represents the space between the tooth of the restraining gear and the locking tooth portion, and “d” represents the outside diameter of the restraining gear.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a magnetic tape cartridge andmore particularly relates, in a magnetic tape cartridge where a singlereel with magnetic tape wound thereon is rotatably housed within acartridge case, to the structure of reel-rotation restraining meanswhich causes the reel to be in a rotation-restrained state when notbeing used.

[0003] 2. Description of the Related Art

[0004] In the magnetic tape cartridges, which are used as storage mediumto be employed in external storage units for computers, etc., there isknown a type where a single tape reel with magnetic tape wound thereonis rotatably housed within a cartridge case. This magnetic tape isemployed as a data archiving tape for computers, etc., and storesimportant information. For this reason, the magnetic tape cartridge isprovided with reel-rotation restraining means for restricting rotationof the reel so that problems, such as tape jamming, etc., do not occurand that the magnetic tape is not pulled out from the cartridge caseunexpectedly when not being used, such as when being archived, etc.

[0005] The reel-rotation restraining means, as disclosed in JapaneseUnexamined Patent Publication No. 11 (1999)-23835, is equipped with arestraining member for restricting rotation of the reel, an urgingmember for urging the restraining member in a restraining direction, andan unlocking member for moving the restraining member in an unlockingdirection in accordance with the chucking operation of the rotationmeans of the drive mechanism of a drive unit such as arecording-reproducing unit.

[0006] A locking tooth portion is formed on the reel side, while arestraining gear meshable with the locking tooth portion is provided onthe side of the restraining member provided so that it cannot rotatewith respect to the cartridge case. In the non-operative state, therestraining gear of the restraining member engages the locking toothportion of the reel to restrict unexpected rotation of the reel, wherebythe magnetic tape wound on the reel can be locked. On the other hand, ifthe magnetic tape cartridge is loaded into the drive unit, the unlockingmember moves the restraining member to disengage the restraining gear ofthe restraining member from the locking tooth portion of the reel. Inthe disengaged or unlocked state, the reel is rotatable and thereforethe magnetic tape can be loaded into or unloaded from the drive unit.

[0007] The above-mentioned unlocking member is equipped with a main bodywhich abuts the above-mentioned restraining member, and leg portionswhich abut the rotation means of the drive mechanism of the drive unit.When the chucking operation of the rotation means is performed, therotation means moves the unlocking member upward to disengage theretraining gear of the restraining member from the locking tooth portionof the reel.

[0008] In the case where a magnetic tape cartridge is equipped with thereel-rotation restraining means mentioned above, incidentally, therestraining member in the unlocked state is unstable because the centralportion of the restraining member is supported only by the centralportion of the unlocking member. On the other hand, because the reel isrotated or stopped according to loading or unloading of the magnetictape, the force exerted on the reel is transmitted to the restrainingmember through the unlocking member. For this reason, the restrainingmember tends to tilt. If the restraining member tilts, the restraininggear thereof will contact the locking tooth portion of the reel. Thisproduces an undesirable sound, disturbs rotation of the reel, andinterferes with the operation of loading or unloading magnetic tape.

[0009] In addition, in the case where the magnetic tape slackens becauseof the shock produced by the magnetic tape cartridge falling when notbeing used, the magnetic tape cartridge cannot absorb the slack of themagnetic tape because it has only a single reel within the cartridgecase. As a result, there is a fear that the magnetic tape will bedamaged. Hence, in order to prevent the magnetic tape from slackeningbecause of shock caused by the cartridge falling, the locking toothportion of the reel and the restraining gear are constructed so that thetooth face of the locking tooth portion, which faces in the reversewinding direction (tape slackening direction), and the tooth face of therestraining gear, which abuts the tooth face of the locking toothportion, are inclined at an angle near to 90 degrees.

[0010] However, in the case where the reel in the non-operative state isunexpectedly locked by the mesh between the restraining gear and thelocking tooth portion, there are cases where the reel is freely moved bythe complete mesh between the restraining gear and the locking toothportion, depending on the phase relationship between the two in theunmeshed state. Particularly, if the tooth face of the locking toothportion, which faces in the reverse winding direction (tape slackeningdirection), and the tooth face of the restraining gear, which abuts thetooth face of the locking tooth portion, are inclined at an angle nearto 90 degrees in order to prevent slackness, as described above, thelocking tooth portion and the restraining gear move only in the windingdirection when they mesh with each other, and consequently, force isexerted on the magnetic tape in the winding direction.

[0011] In addition, in the case of a magnetic tape cartridge withmagnetic tape wound on a single reel, a tape leader member is coupledwith the leading end of the magnetic tape, and the tape leader member iscaught by the catching member of the drive mechanism of a drive unit topull out the magnetic tape from the cartridge case. In thisconstruction, if the tape leader member is exposed to the caseperipheral side, there is a problem that the free end will project fromthe cartridge case, or dust will enter the cartridge case through a tapeleader opening formed in the cartridge case, when the magnetic tapecartridge is subjected to a falling shock, etc. Hence, it is disclosedin Japanese Unexamined Patent Publication No.11(1999)-232828 that a tapeleader pin is retained inside a tape leader opening which is closed oropened by a slide door. The configuration of the tape leader member isdetermined mainly by specifications for the recording-reproducing unit.

[0012] Thus, in the case where the tape leader pin is coupled with theleading end of the magnetic tape, and the tape leader pin is retainedwithin the cartridge case during the non-operative state, if the reel ismoved in the winding direction and a pulling force greater than apredetermined quantity is exerted on the magnetic tape, there is a fearthat the magnetic tape and the tape leader pin will be easily disengagedfrom each other, because the strength of the engagement of the tapeleader pin with the magnetic tape is relatively low. Even when the twoare not disengaged, the magnetic tape will be stretched by theaforementioned pulling force. Because of this, the magneticrecording-reproducing characteristics are degraded, or the tape leaderpin is shifted out of a predetermined retaining position or tilted.Thereafter, there is a fear that the magnetic tape cannot be correctlyloaded into the drive unit and therefore reliability will be reduced.

SUMMARY OF THE INVENTION

[0013] The present invention has been made in view of theabove-mentioned points. Accordingly, it is a first important object ofthe present invention to provide a magnetic tape cartridge which iscapable of preventing the contact between a restraining gear and alocking protrusion that is caused by the tilt of the restraining member.

[0014] A second important object of the invention is to provide amagnetic tape cartridge that is capable of preventing the disengagementof the magnetic tape from a tape leader pin which is caused by themagnetic tape pulled in the locked state when subjected to a fallingshock, while assuring the locked state of a reel obtained in anon-operative by the restraining member of reel-rotation restrainingmeans.

[0015] To achieve the first object of the present invention and inaccordance with the present invention, there is provided a firstmagnetic tape cartridge comprising:

[0016] a cartridge case where a single reel with magnetic tape woundthereon is rotatably housed; and

[0017] reel-rotation restraining means which, when not used, goes to alocked state to restrict rotation of the reel and, when used, goes fromthe locked state to an unlocked state to allow the rotation; thereel-rotation restraining means having a restraining member forrestricting rotation of the reel by moving toward or away from the reel,an urging member for urging the restraining member in a restrainingdirection, and an unlocking member for moving the restraining member inan unlocking direction, by rotating integrally with the reel and movingaccording to a chucking operation of rotation means of a drive unit;

[0018] wherein the restraining member has a restraining gear whichmeshes with a locking tooth portion formed in the reel to restrainrotation of the reel, the restraining member being supported by asupport portion of the cartridge case so that it is slidable withoutbeing rotated; and

[0019] the following relationship is met:

b≦(2×a×c)/d

[0020] where “a” represents the length of engagement between therestraining member in the unlocked state and the support portion, “b”represents the clearance between the restraining member and the supportportion, “c” represents the space between a tooth of the restraininggear and the locking tooth portion, and “d” represents the outsidediameter of the restraining gear.

[0021] In accordance with the present invention, there is provided asecond magnetic tape cartridge comprising:

[0022] a cartridge case where a single reel with magnetic tape woundthereon is rotatably housed; and

[0023] reel-rotation restraining means which, when not used, goes to alocked state to restrict rotation of the reel and, when used, goes fromthe locked state to an unlocked state to allow the rotation; thereel-rotation restraining means having a restraining member forrestricting rotation of the reel by moving toward or away from the reel,an urging member for urging the restraining member in a restrainingdirection, and an unlocking member for moving the restraining member inan unlocking direction, by rotating integrally with the reel and movingaccording to a chucking operation of rotation means of a drive unit;

[0024] wherein the reel has a reel gear which meshes with a driving gearof drive means of the drive unit;

[0025] the unlocking member has a main body which abuts the restrainingmember, and leg portions whose lower ends abut part of the drive meansof the drive unit through guide holes provided to penetrate the reelgear; and

[0026] in the locked state, the lower ends of the leg portions of theunlocking member project from a tooth edge of the reel gear.

[0027] In accordance with the present invention, there is provided athird magnetic tape cartridge comprising:

[0028] a cartridge case where a single reel with magnetic tape woundthereon is rotatably housed; and

[0029] reel-rotation restraining means which, when not used, goes to alocked state to restrict rotation of the reel and, when used, goes fromthe locked state to an unlocked state to allow the rotation; thereel-rotation restraining means having a restraining member forrestricting rotation of the reel by moving toward or away from the reel,an urging member for urging the restraining member in a restrainingdirection, and an unlocking member for moving the restraining member inan unlocking direction, by rotating integrally with the reel and movingaccording to a chucking operation of rotation means of a drive unit;

[0030] wherein the restraining member has a restraining gear whichmeshes with a locking tooth portion formed in the reel to restrainrotation of the reel, the restraining member being supported by asupport portion of the cartridge case so that it is slidable withoutbeing rotated; and

[0031] in the unlocked state, the space between a tooth of therestraining gear and the locking tooth portion is set to a lengthgreater than or equal to a tooth depth of the restraining gear.

[0032] In the third magnetic tape cartridge, it is preferable that theaforementioned space be set greater than or equal to 1.2 times the toothdepth of the restraining gear. It is further preferable that theaforementioned space be set greater than or equal to 1.4 times the toothdepth of the restraining gear.

[0033] In accordance with the present invention, there is provided afourth cartridge case where a single reel with magnetic tape woundthereon is rotatably housed; and

[0034] reel-rotation restraining means which, when not used, goes to alocked state to restrict rotation of the reel and, when used, goes fromthe locked state to an unlocked state to allow the rotation; thereel-rotation restraining means having a restraining member forrestricting rotation of the reel by moving toward or away from the reel,an urging member for urging the restraining member in a restrainingdirection, and an unlocking member for moving the restraining member inan unlocking direction, by rotating integrally with the reel and movingaccording to a chucking operation of rotation means of a drive unit;

[0035] wherein either a slide portion of the restraining member or aslide portion of the unlocking member is formed into a curved surfacewhich has a radius of curvature of 30 mm or less.

[0036] In the fourth magnetic tape cartridge, it is preferable that theradius of curvature of the curved surface be 20 mm or less. It isfurther preferable that the radius of curvature of the curved surface be15 mm or less.

[0037] In accordance with the present invention, there is provided afifth magnetic tape cartridge comprising:

[0038] a cartridge case where a single reel with magnetic tape woundthereon is rotatably housed; and

[0039] reel-rotation restraining means which, when not used, goes to alocked state to restrict rotation of the reel and, when used, goes fromthe locked state to an unlocked state to allow the rotation; thereel-rotation restraining means having a restraining member forrestricting rotation of the reel by moving toward or away from the reel,an urging member for urging the restraining member in a restrainingdirection, and an unlocking member for moving the restraining member inan unlocking direction, by rotating integrally with the reel and movingaccording to a chucking operation of rotation means of a drive unit;

[0040] wherein the restraining member has a restraining gear whichmeshes with a locking tooth portion formed in the reel to restrainrotation of the reel;

[0041] the urging member is supported by a spring receiver formed in thecartridge case; and

[0042] the following relationship is met:

e≦(2×f×c)/d

[0043] where “c” represents the space between a tooth of the restraininggear in the unlocked state and the locking tooth portion, “d” representsthe outside diameter of the restraining gear, “e” represents theclearance between an outer periphery of the urging member and an innerperiphery of the spring receiver, and “f” represents the length ofengagement between the urging member and the spring receiver.

[0044] To achieve the aforementioned second object of the presentinvention and in accordance with the present invention, there isprovided a sixth magnetic tape cartridge comprising:

[0045] a cartridge case where a single reel with magnetic tape woundthereon is rotatably housed; and

[0046] reel-rotation restraining means which, when not used, goes to alocked state to restrict rotation of the reel and, when used, goes fromthe locked state to an unlocked state to allow the rotation; thereel-rotation restraining means having a restraining member forrestricting rotation of the reel by moving toward or away from the reel,an urging member for urging the restraining member in a restrainingdirection, and an unlocking member for moving the restraining member inan unlocking direction, by rotating integrally with the reel and movingaccording to a chucking operation of rotation means of a drive unit;

[0047] wherein the restraining member has a restraining gear whichmeshes with a locking tooth portion formed in the reel to restrainrotation of the reel; and

[0048] a tooth of the restraining gear has two inclined faces which havean apex angle and interior angles, the apex angle being between an apexangle of the locking tooth portion of the reel and 90 degrees, and theinterior angles being 30 degrees or greater with respect to a verticalline and also being approximately the same.

[0049] Note that the aforementioned vertical line refers to a linevertical to the direction of rotation of the reel. Also, in the sixthmagnetic tape cartridge, it is preferable that the locking tooth portionand the tooth of the restraining gear be formed from synthetic resinmaterial.

[0050] The present invention has the following advantages:

[0051] (1) In the reel-rotation restraining means, which has arestraining member for restricting rotation of the reel by moving towardor away from the reel, an urging member for urging the restrainingmember in a restraining direction, and an unlocking member for movingthe restraining member in an unlocking direction, by rotating integrallywith the reel and moving according to a chucking operation of rotationmeans of a drive unit,

[0052] the following relationship is met:

b≦(2×a×c)/d

[0053] where “a” represents the length of engagement between therestraining member in the unlocked state and the support portion, “b”represents the clearance between the restraining member and the supportportion, “c” represents the space between a tooth of the restraininggear and the locking tooth portion, and “d” represents the outsidediameter of the restraining gear; or the following relationship is met:

e≦(2×f×c)/d

[0054] where “c” represents the space between a tooth of the restraininggear in the unlocked state and the locking tooth portion, “d” representsthe outside diameter of the restraining gear, “e” represents theclearance between an outer periphery of the urging member and an innerperiphery of the spring receiver, and “f” represents the length ofengagement between the urging member and the spring receiver. With thisarrangement, tilting of the restraining member is suppressed in theunlocked state. Therefore, the contact between the restraining gear andthe locking tooth portion can be prevented and the major causes of anundesirable sound and a hindrance to the rotation of the reel can beeliminated.

[0055] (2) In the locked state, the lower ends of the leg portions ofthe unlocking member project from the tooth edge of the reel gear. Also,in the unlocked state, the space between the tooth of the restraininggear and the locking tooth portion is set to a length greater than orequal to the tooth depth of the restraining gear. With this arrangement,the extent of movement of the restraining member in the unlocked stateincreases. Therefore, even if the restraining member tilts slightly, thecontact between the restraining gear and the locking tooth portion canbe prevented and the major causes of an undesirable sound and ahindrance to the rotation of the reel can be eliminated.

[0056] (3) Either a slide portion of the restraining member or a slideportion of the unlocking member is formed into a curved surface whichhas a radius of curvature of 30 mm or less. With this, when therestraining member tilts, restoring force to a flat state that equalizesthe urging force produced by the urging member in the circumferentialdirection is enhanced and tilting of the restraining member issuppressed. Therefore, the contact between the restraining gear and thelocking protrusion can be prevented and the major causes of anundesirable sound and a hindrance to the rotation of the reel can beeliminated.

[0057] (4) The tooth of the restraining gear has two inclined faceswhich have an apex angle and interior angles, the apex angle beingbetween an apex angle of the locking tooth portion of the reel and 90degrees, and the interior angles being 30 degrees or greater withrespect to a vertical line and also being approximately the same. Thatis, the interior angles are within 45 degrees. With this, in the meshedstate between the restraining gear and the locking tooth portion, thereel can be reliably locked. Even if the two are shifted in phase whenlocked and therefore the reel is moved in the reverse winding direction,the extent of movement will be slight and therefore the slack of themagnetic tape will also be slight. Also, even if the reel is moved inthe winding direction because of the mesh between the two, the extent ofmovement will be slight and therefore a pulling force that is exerted onthe magnetic tape by the movement of the reel 2 will be small.Therefore, the disengagement of the magnetic tape from the tape leaderpin due to forced locking can be prevented.

[0058] (5) When the reel is rotated in the winding direction by fallingshock, etc., and an excessive pulling force is exerted on the magnetictape, the restraining member is moved in the unlocking direction by theinclined face of the locking tooth portion which faces in the reversewinding direction. As a result, the meshed state between the restrainingmember and the locking tooth portion becomes shallow and the rotation ofthe reel in the reverse winding direction is allowed. Therefore, anexcessive pulling force can be alleviated and the disengagement of themagnetic tape from the tape leader pin can be prevented.

[0059] (6) The apex angle of the tooth of the restraining gear of therestraining member is set to an angle greater than the apex angle of thelocking tooth portion of the reel. That is, the tooth edge of thelocking tooth portion of the reel is made thinner by setting the apexangle of the locking tooth portion to an angle less than the apex angleof the tooth of the restraining gear of the restraining member. As aresult, the locking tooth portion becomes easy to deform, and slightplay can be provided between the teeth. Therefore, a force to pull themagnetic tape can be alleviated without reducing the forced lockingfunction. Particularly, in the case where the restraining gear and thelocking tooth portion are formed from synthetic resin material, thefunction of alleviating the pulling force to be exerted on the magneticforce is enhanced because they are easily deformable.

[0060] (7) Thus, according to the present invention, reliable locking ofthe reel in the non-operative state, and alleviation of a magnetic-tapepulling force that is produced in the locked state by falling shock,etc., are compatible with each other. This can enhance reliability,while preventing stretching and disengagement of the magnetic tape andassuring magnetic recording-reproducing characteristics and a correctoperation of loading the magnetic tape.

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The present invention will be described in further detail withreference to the accompanying drawings wherein:

[0062]FIG. 1 is a front sectional view of a magnetic tape cartridge ofan embodiment of the present invention in the non-operative state;

[0063]FIG. 2 is a part-sectional view of the essential parts of themagnetic tape cartridge of FIG. 1 in the operative state;

[0064]FIG. 3 is a part-sectional view taken substantially along line A-Aof FIG. 2;

[0065]FIG. 4 is a part-sectional view showing the tilted state of therestraining member shown in FIG. 2;

[0066]FIG. 5 is a part-sectional view showing the positionalrelationships between parts, obtained according to a form forsuppressing the tilt of the restraining member;

[0067]FIG. 6 is a part-sectional view showing the positionalrelationships between parts, obtained according to another form forsuppressing the tilt of the restraining member; and

[0068]FIG. 7 is an enlarged sectional view taken substantially alongline B-B of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0069] Referring to FIG. 1, there is shown a preferred embodiment of amagnetic tape cartridge in accordance with the present invention. Themagnetic tape cartridge 1 is equipped with a cartridge case 3, which isformed by fastening an upper case 31 and a lower case 32 together withsmall screws, etc. The lower case 32 is provided at a center portionthereof with an opening 32 a. A single reel 2 with magnetic tape (notshown) wound thereon is housed rotatably within the cartridge case 3.The magnetic tape cartridge 1 is further equipped with reel-rotationrestraining means 10, which allows rotation of the reel 2 when beingused and restricts the rotation when not being used.

[0070] The reel 2 consists of a bottomed cylindrical reel hub 21, wheremagnetic tape is wound on the outer periphery, and upper and lowerflange portions 22 and 23 respectively projected in disk form in theradial direction from the upper and lower ends of the outer periphery ofthis reel hub 21. The reel hub 21 and the lower flange portion 22 areintegrally formed from synthetic resin and are united with the upperflange portion 23, for example, by ultrasonic welding. The reel hub 21is closed at a lower portion thereof by a bottom wall 21 a. The radiallyouter portion of the bottom surface of the bottom wall 21 a has anannular reel gear 24 that meshes with the driving gear 13 of rotationmeans 11 provided in a cartridge drive mechanism (not shown). A reelplate 25 for magnetic suction is formed from an annular metal plate andis attached inside the reel gear 24. The reel gear 24 and reel plate 25of the reel 2 are disposed to face the opening 32 a in the bottomsurface of the cartridge case 3. Note that the reel 2 is urged downwardby an urging member 5 to be described later.

[0071] On the other hand, the rotation means 11 of the cartridge drivemechanism is equipped on the upper end surface of a rotating shaft 12with the annular driving gear 13 and a driving magnet (not shown). Inthe chucking operation, the magnetic tape cartridge 1 loaded into abucket (not shown) on the driving side is lowered toward the rotatingshaft 12. Then, the driving gear 13 meshes with the reel gear 24, andthe reel plate 25 inside the reel gear 24 is attracted by the drivingmagnet provided inside the riving gear 13, whereby the meshed statebetween the driving gear 13 and the reel gear 24 is held.

[0072] Next, a description will be given of the mechanism of thereel-rotation restraining means 10. This reel-rotation restraining means10 is equipped with a restraining member 4 movable toward or away fromthe reel 2 in an up-and-down direction; an urging member 5, formed froma coil spring, for urging the restraining member 4 in a restrainingdirection; and an unlocking member 6 for moving the restraining member 4in an unlocking direction.

[0073] Three guide holes 26 penetrating the reel gear 24 in theup-and-down direction are disposed in the bottom wall 21 a of the reel 2at regular intervals on a circle (see FIG. 4). Furthermore, three pairsof locking protrusions (i.e., 6 locking protrusions) 27 are erected inthe top surface of the bottom wall 21 a at regular intervals on a circleat positions different in phase from the guide holes 26 (see FIG. 3).The upper end portion of each locking protrusion 27 is formed into alocking tooth portion 29. Note that three or more guide holes 26 may bedisposed. Also, three or more pairs of locking protrusions 27 may bedisposed. Furthermore, the locking tooth portion 29 of the upper end ofthe locking protrusion 27 may be constructed of a single tooth.

[0074] The restraining member 4, formed from synthetic resin material,has a disc portion 41 within the reel hub 21 of the reel 2. The discportion 41 is disposed to face the bottom wall 21 a of the reel 2. Arestraining gear 42 is formed in annular form in the radially outerportion of the bottom surface of the disc portion 41 and is meshablewith the locking tooth portion 29 of the locking protrusions 27. Inaddition, the center portion of the bottom surface of the disc portion41 is projected downward and formed into a slide portion 41 a. The slideportion 41 a is engageable with the slide portion 61 a of the topsurface of the main portion 61 of the unlocking member 6 to be describedlater by the urging force of the urging member 5 of the reel-rotationrestraining means 10.

[0075] Furthermore, a protruding portion 44 extends upward from the topsurface of the disc portion 41 of the restraining member 4. Theprotruding portion 44 is provided with a stopper groove 45 in the formof a cross, which extends in the up-and-down direction. On the otherhand, a support portion (swivel stopping protrusion) 33 that is insertedinto the stopper groove 45 is erected in the inside surface of the uppercase 31 of the cartridge case 3. If the stopper groove 45 and thesupport portion 33 are engaged with each other, the restraining member 4can move in the up-and-down direction without rotating. While thesupport portion 33 in this embodiment is provided inside the restrainingmember 4, it may be provided outside the restraining member 4.

[0076] The urging member (e.g., a coil spring) 5 is interposed betweenthe top surface, outside the protruding portion 44, of the disc portion41 of the restraining member 4 and the inside surface, outside thesupport portion 33, of the upper case 3. The urging member 5 is used forurging the restraining member 4 downward in the locking direction wherethe restraining gear 42 and the locking tooth portion 29 engage witheach other.

[0077] The unlocking member 6 is interposed between the restrainingmember 4 and the bottom wall 21 a of the reel hub 21 so that it ismovable up and down. For this reason, three cylindrical leg portions 63extending in the up-and-down direction are provided on the bottomsurface of the triangular main body 61 corresponding to the vertexes ofthe main body 61. The leg portions 63 are inserted into the guide holes26 of the bottom wall 21 of the reel 2 so that they are movable into andout of the guide holes 26. The lower ends of the leg portions 63 arelocated to face the tooth portion of the reel gear 24 of the bottomsurface of the reel 2. With the leg portions 63 inserted into the guideholes 26, each pair of locking protrusions 27 is located between twoadjacent leg portions 63 and outside the main body 61 of the unlockingmember 6. Note that the leg portion 63 may be formed into the shape of asquare pillar, an elliptic cylinder, etc.

[0078] When the unlocking member 6 is at the lowest position (see FIG.1), the lower ends of the leg portions 63 of the unlocking member 6project from the reel gear 24. When, at the lowest position, the drivinggear 13 is meshed with the reel gear 24 by the chucking operation of therotation means 11 of the cartridge drive mechanism (not shown), theunlocking member 6 is pushed upward by a predetermined quantity ofstroke (see FIG. 2). Also, the unlocking member 6 is rotated integrallywith the reel 2 by the fit of the leg portions 63 into the guide holes26.

[0079] The reel 2 is provided with guide members 28 for guiding part ofthe unlocking member 6 in the direction of insertion when inserting theleg portions 63 of the unlocking member 6 into the guide holes 26 (seeFIG. 3) Each guide member 28 is formed on the inside wall, near theguide hole 26, of the reel hub 21 of the reel 2 and is constructed oftwo guide ribs, which extend in the up-and-down direction (i.e., thedirection in which the leg portions 63 are inserted), for guiding thevertex of the triangular main body 61 of the unlocking member 6. Also,similar reinforcement ribs are disposed over the inner peripheralsurface of the reel hub 21.

[0080] In the unlocked state of the reel-rotation restraining means 10,incidentally, the restraining member 4 is unstable and tends to tilt,because only the central portion of the bottom surface of therestraining member 4 is in contact with the central portion of theunlocking member 6. On the other hand, since the reel 2 is rotated orstopped when magnetic tape is loaded or unloaded, the force produced bythe loading or unloading operation is exerted on the restraining member4 through the unlocking member 6. Therefore, if the restraining member 4is tilted as shown in FIG. 4 by the produced force, the restraining gear42 of the restraining member 4 will be brought into contact with thelocking tooth portion 29 of the reel 2 and will produce an undesirablesound. Because of this, rotation of the reel 2 is disturbed and theoperation of loading or unloading magnetic tape cannot be performed withstability.

[0081] Hence, in the present invention, a structure for suppressing thetilt of the restraining member 4 that is in the unlocked state isadopted in the reel-rotation restraining means 10. As a first form ofthe tilt suppressing structure, in a stopper structure, which isconstructed of the stopper groove 45 of the protruding portion 44 andthe support portion 33 of the upper case 31, for supporting therestraining member 4 on the upper case 31 so that it is movable in theup-and-down direction without rotating, as shown in FIG. 5, thefollowing dimensional relationship is met:

b≦(2×a×c)/d

[0082] where “a” represents the length of engagement between therestraining member 4 and the support portion 33 of the upper case 31,“b” represents the clearance between the restraining member 4 and thesupport portion 33, “c” represents the space between the restraininggear 42 and the locking tooth portion 29 of the locking protrusion 27,and “d” represents the outside diameter of the restraining gear 42.

[0083] That is, the clearance b between the restraining member 4 and thesupport portion 33 is set narrow to the degree that contact between therestraining gear 42 and the locking tooth portion 29 does not occur.

[0084] From the aforementioned Equation, the length of engagementbetween the restraining member 4 and the upper case is set long so thatit meets the following dimensional relationship:

a≧(b×d)/(2×c).

[0085] As a second form of the tilt suppressing structure, in the caseof providing the urging member 5 formed from a coil spring, as shown inFIG. 6, the following dimensional relationship is set in order tosuppress the tilt of the restraining member 4 by regulating the tilt ofthe urging member 5 with respect to a spring receiver 34 formed on theinside surface of the upper case 31:

e≦(2×f×c)/d

[0086] where “c” represents the space in the unlocked state between therestraining gear 42 and the locking tooth portion 29, “d” represents theoutside diameter of the restraining gear 42, “e” represents theclearance between the outer periphery of the urging member 5 and theinner periphery of the spring receiver 34, and “f” represents the lengthof engagement between the urging member 5 and the spring receiver 34.

[0087] That is, the clearance “e” between the restraining member 4 andthe support portion 33 is set narrow to the degree that the contactbetween the restraining gear 42 and the locking tooth portion 29 doesnot occur. The urging force of the urging member 5 in thecircumferential direction is equalized, so the restraining member 4 canbe held parallel. Also, the engagement length “f” between the urgingmember 5 and the spring receiver 34 is made long so that it meets theaforementioned Equation.

[0088] As a third form of the tilt suppressing structure, the slideportion 41 a of the restraining member 4 that slides on the slideportion 61 a of the unlocking member 6 has a curved surface, which has aradius of curvature (R) of 30 mm or less. It is preferable that theradius of curvature (R) be 20 mm or less and further preferable that itbe 15 mm or less. With this, the restraining member 4 is liable toreturn to a flat state if the radius of curvature is smaller, when therestraining member 4 returns to the flat state by oscillation of theslide portion 41 a caused when the circumferential urging force producedby the urging member 5 becomes unequal because of the tilt of therestraining member 4.

[0089] As a fourth form of the tilt suppressing structure, the lower endof the leg portion 63 of the unlocking member 6 in the locked state isprovided to project from the lower end (addendum circle) of the reelgear 24, because the space between the restraining gear 42 and thelocking tooth portion 29 becomes large and the allowable tilt angle ofthe restraining member 4 can be made large, if the quantity of movementof the unlocking member 6 is increased when the unlocking operation isperformed (see FIG. 1). With this arrangement, when the driving gear 13meshes with the reel gear 24, the leg portions 63 of the unlockingmember 6 are pushed up before the driving gear 13 meshes with the reelgear 24. For this reason, the extent to which the leg portions 63 arepushed up until the driving gear 13 completely meshes with the reel gear24, that is, the extent of movement of the unlocking member 6 becomeslarge. Therefore, the space between the restraining gear 42 and thelocking protrusion 27 becomes large in the unlocked state.

[0090] As a fifth form of the tilt suppressing structure, in order tosimilarly make the space between the restraining gear 42 and the lockingprotrusion 27 larger in the unlocked state, the slide portion 41 a ofthe restraining member 4 and the slide portion 61 a of the unlockingmember 6 are provided so that they contact each other in the lockedstate shown in FIG. 1. That is, the restraining member 4 at the loweredposition (locked state) does not always need to abut the unlockingmember 6, because the restraining gear 42 meshes with the locking toothportion 29 and is stopped. However, if there is clearance between therestraining member 4 and the unlocking member 6 when the unlockingmember 6 moves in the unlocking direction, the quantity of movement ofthe restraining member 4 is reduced by the quantity of the clearancewith respect to the quantity of movement of the unlocking member 6.Therefore, if the restraining member 4 and the unlocking member 6 are incontact with each other in the locked state, the gap between therestraining gear 42 and the locking tooth portion 29 can be made largerin the unlocked state, while assuring the extent of movement of therestraining member 4.

[0091] As a sixth form of the tilt suppressing structure, in order tomake the gap between the restraining gear 42 and the locking toothportion 29 larger in the unlocked state even if the extent of movementof the restraining member 4 during the unlocking operation is the same,the space “c” between the restraining gear 42 and the locking toothportion 29 is set greater than or equal to the whole depth “t” of therestraining gear 42 (see FIG. 5). That is, the relationship between cand t is set to c≧t. It is preferable that the relationship be c≧1.2tand further preferable that it be c≧1.4t. If teeth are the same inshape, increasing the number of teeth of the restraining gear 42 canreduce the whole tooth depth “t” and make the aforementioned space “c”larger. Therefore, when the restraining member 4 tilts slightly, thecontact between the restraining gear 42 and the locking tooth portion 29can be prevented. In addition, a reduction in the pitch between adjacentteeth in the restraining gear 42 reduces slackening or stretching ofmagnetic tape in the locked state.

[0092] Note that practically, the aforementioned various tiltsuppressing forms are constructed in combination so that the tilt of therestraining member 4 is prevented.

[0093] Furthermore, in the present invention, the reel-rotationrestraining means adopts a structure for preventing the disengagement ofthe magnetic tape from a tape leader pin which is caused by the magnetictape pulled in the locked state by falling shock, etc.

[0094] The restraining gear 42 of the restraining member 4 and thelocking tooth portion 29 have a triangular cross section, as illustratedin FIG. 7. Each tooth of the locking tooth portion 29 on the side of thereel 2 has a front inclined face 29 b which faces in the windingdirection (indicated by an arrow W) and a rear inclined face 29 a whichfaces in the reverse winding direction (indicated by an arrow U). On theother hand, each tooth of the restraining gear 42 on the restrainingmember 4 has a front inclined face 42 a which abuts the rear inclinedface 29 a of the locking tooth portion 29 when the reel 2 is rotated inthe reverse winding direction (indicated by an arrow U), and a rearinclined face 42 b which abuts the front inclined face 29 b when thereel 2 is rotated in the winding direction (indicated by an arrow W).

[0095] In the tooth of the restraining gear 42, the apex angle γ iswithin 90 degrees, the interior angle α of the front inclined face 42 awith respect to a vertical plane “s” is 30 degrees or greater, theinterior angle β of the rear inclined face 42 a with respect to thevertical plane “s” is 30 degrees or greater, and α and β areapproximately the same. In the tooth of the locking tooth portion 29, aswith the tooth of the restraining gear 42, the apex angle γ′ is within90 degrees, the interior angle α′ of the rear inclined face 29 a withrespect to a vertical plane s′ is 30 degrees or greater, the interiorangle β′ of the front inclined face 29 a with respect to the verticalplane s′ is 30 degrees or greater, and α′ and β′ are approximately thesame. However, γ is greater than or equal to γ′. That is, therestraining gear 42 and the locking tooth portion 29 are formed in arange of 60°≦γ′≦γ≦90° and 30°≦α, β, α′, β′≦45°.

[0096] Note that the restraining gear 42 and the locking tooth portion29 are formed in conical form so that the whole tooth depth of the outerperipheral portion becomes higher. Thus, the outer peripheral portionsmesh each other earlier.

[0097] Now, a description will be given of the operation of thereel-rotation restraining means 10. In a non-operative state, such as anarchived state, etc., of the magnetic tape cartridge 1 shown in FIG. 1,the restraining member 4, the unlocking member 6, and the reel 2 aremoved to the side of the lower case 32 of the cartridge case 3 by theurging force of the urging member 5. The center opening 32 a in thelower case 32 is closed by the reel 2. The unlocking member 6 is at thelowered position where the bottom surface abuts the top surface of thebottom wall 21 a of the reel hub 21. The lower ends of the leg portions63 of the unlocking member 6 project from the tooth edge of the reelgear 24. The restraining member 4 abutting the top surface of theunlocking member 6 is also at its lowered position. The locking toothportion 29 of the reel 2 mesh with the restraining gear 42 of therestraining member 4. Thus, the restraining member 4 restricts rotationof the reel 2 and is in a locked state of preventing the operation ofloading the magnetic tape.

[0098] On the other hand, in the operative state of FIG. 2 in which themagnetic tape cartridge 1 is loaded into the drive mechanism of therecording-reproducing unit, the rotating shaft 12 of the rotation means11 approaches the bottom surface of the reel 2. Also, the driving gear13 meshes with the reel gear 24 and moves and holds the reel 2 slightlyupward. Then, the tooth edges of the driving gear 13 abut the lower endsof the leg portions 63 of the unlocking member 6 and push them up. As aresult, the unlocking member 6 moves upward against the urging force ofthe urging member 5, and the restraining member 4, along with thisunlocking member 6, also moves in the upward unlocking direction. Thisunlocks the engagement between the teeth of the restraining gear 42 andthe locking tooth portion 29, whereby the reel 2 becomes free to rotate.In this unlocked state, the magnetic tape is loaded or unloaded by thedrive mechanism of the recording-reproducing unit.

[0099] In the locked state, the tilt of the restraining member 4 issuppressed or removed by adopting the aforementioned various forms ofthe tilt suppressing structure. Also, the gap between the restraininggear 42 and the locking tooth portion 29 is made larger in the unlockedstate. Therefore, the contact between the restraining gear 42 and thelocking tooth portion 29 is prevented, the occurrence of an undesirablesound is prevented, and a hindrance to rotation of the reel 2 isprevented. In this manner, the magnetic tape can be rotated withoutbeing subjected to a load of some magnitude.

[0100] In addition, since the interior angels α and β of the inclinedfaces of each tooth of the restraining gear 42 and the interior anglesα′ and β′ of each tooth of the locking tooth portion 29 is set between30 and 45 degrees, the reel 2 can be reliably locked in the meshed statebetween the restraining gear 42 and the locking tooth portion 29.Furthermore, even if the restraining gear 42 and the locking toothportion 29 are shifted in phase from each other when they are locked,the extent of movement due to the mesh between the restraining gear 42and the locking tooth portion 29 will be slight in the reverse windingdirection and the winding direction. The slack of the magnetic tape isalso slight, so a pulling force that is exerted on the magnetic tape bythe movement of the reel 2 in the winding direction W is small.Therefore, the disengagement of the magnetic tape from a tape leader pindue to forced locking can be prevented.

[0101] When, in the aforementioned locked state, the reel 2 is rotatedin the winding direction W by falling shock, etc., and an excessivepulling force is exerted on the magnetic tape, the restraining member 4is moved upward in the unlocking direction against the urging member 5by the inclined faces 42 a and 29 a of the restraining gear 42 and thelocking tooth portion 29 which face in the reverse winding direction U,because the interior angles of the inclined surface 42 a and 29 a are 30degrees or greater. With the upward movement of the restraining member4, the restraining gear 42 and the locking tooth portion 29 aredisengaged from each other and the reel 2 is rotated in the reversewinding direction U, that is, the tape slackening direction, so pullingforce is reduced and alleviated. Thus, stretching and disengagement ofthe magnetic tape can be prevented.

[0102] While the present invention has been described with reference tothe preferred embodiments thereof, the invention is not to be limited tothe details given herein, but may be modified within the scope of theinvention hereinafter claimed.

What is claimed is:
 1. A magnetic tape cartridge comprising: a cartridge case where a single reel with magnetic tape wound thereon is rotatably housed; and reel-rotation restraining means which, when not used, goes to a locked state to restrict rotation of said reel and, when used, goes from said locked state to an unlocked state to allow said rotation; said reel-rotation restraining means having a restraining member for restricting rotation of said reel by moving toward or away from said reel, an urging member for urging said restraining member in a restraining direction, and an unlocking member for moving said restraining member in an unlocking direction, by rotating integrally with said reel and moving according to a chucking operation of rotation means of a drive unit; wherein said restraining member has a restraining gear which meshes with a locking tooth portion formed in said reel to restrain rotation of said reel, said restraining member being supported by a support portion of said cartridge case so that it is slidable without being rotated; and the following relationship is met: b≦(2×a×c)/d where “a” represents the length of engagement between said restraining member in said unlocked state and said support portion, “b” represents the clearance between said restraining member and said support portion, “c” represents the space between a tooth of said restraining gear and said locking tooth portion, and “d” represents the outside diameter of said restraining gear.
 2. A magnetic tape cartridge comprising: a cartridge case where a single reel with magnetic tape wound thereon is rotatably housed; and reel-rotation restraining means which, when not used, goes to a locked state to restrict rotation of said reel and, when used, goes from said locked state to an unlocked state to allow said rotation; said reel-rotation restraining means having a restraining member for restricting rotation of said reel by moving toward or away from said reel, an urging member for urging said restraining member in a restraining direction, and an unlocking member for moving said restraining member in an unlocking direction, by rotating integrally with said reel and moving according to a chucking operation of rotation means of a drive unit; wherein said reel has a reel gear which meshes with a driving gear of drive means of said drive unit; said unlocking member has a main body which abuts said restraining member, and leg portions whose lower ends abut part of said drive means of said drive unit through guide holes provided to penetrate said reel gear; and in said locked state, the lower ends of said leg portions of said unlocking member project from a tooth edge of said reel gear.
 3. A magnetic tape cartridge comprising: a cartridge case where a single reel with magnetic tape wound thereon is rotatably housed; and reel-rotation restraining means which, when not used, goes to a locked state to restrict rotation of said reel and, when used, goes from said locked state to an unlocked state to allow said rotation; said reel-rotation restraining means having a restraining member for restricting rotation of said reel by moving toward or away from said reel, an urging member for urging said restraining member in a restraining direction, and an unlocking member for moving said restraining member in an unlocking direction, by rotating integrally with said reel and moving according to a chucking operation of rotation means of a drive unit; wherein said restraining member has a restraining gear which meshes with a locking tooth portion formed in said reel to restrain rotation of said reel, said restraining member being supported by a support portion of said cartridge case so that it is slidable without being rotated; and in said unlocked state, the space between a tooth of said restraining gear and said locking tooth portion is set to a length greater than or equal to a tooth depth of said restraining gear.
 4. The magnetic tape cartridge as set forth in claim 3, wherein said space is set greater than or equal to 1.2 times the tooth depth of said restraining gear.
 5. The magnetic tape cartridge as set forth in claim 3, wherein said space is set greater than or equal to 1.4 times the tooth depth of said restraining gear.
 6. A magnetic tape cartridge comprising: a cartridge case where a single reel with magnetic tape wound thereon is rotatably housed; and reel-rotation restraining means which, when not used, goes to a locked state to restrict rotation of said reel and, when used, goes from said locked state to an unlocked state to allow said rotation; said reel-rotation restraining means having a restraining member for restricting rotation of said reel by moving toward or away from said reel, an urging member for urging said restraining member in a restraining direction, and an unlocking member for moving said restraining member in an unlocking direction, by rotating integrally with said reel and moving according to a chucking operation of rotation means of a drive unit; wherein either a slide portion of said restraining member or a slide portion of said unlocking member is formed into a curved surface which has a radius of curvature of 30 mm or less.
 7. The magnetic tape cartridge as set forth in claim 6, wherein the radius of curvature of said curved surface is 20 mm or less.
 8. The magnetic tape cartridge as set forth in claim 6, wherein the radius of curvature of said curved surface is 15 mm or less.
 9. A magnetic tape cartridge comprising: a cartridge case where a single reel with magnetic tape wound thereon is rotatably housed; and reel-rotation restraining means which, when not used, goes to a locked state to restrict rotation of said reel and, when used, goes from said locked state to an unlocked state to allow said rotation; said reel-rotation restraining means having a restraining member for restricting rotation of said reel by moving toward or away from said reel, an urging member for urging said restraining member in a restraining direction, and an unlocking member for moving said restraining member in an unlocking direction, by rotating integrally with said reel and moving according to a chucking operation of rotation means of a drive unit; wherein said restraining member has a restraining gear which meshes with a locking tooth portion formed in said reel to restrain rotation of said reel; said urging member is supported by a spring receiver formed in said cartridge case; and the following relationship is met: e≦(2×f×c)/d where “c” represents the space between a tooth of said restraining gear in said unlocked state and said locking tooth portion, “d” represents the outside diameter of said restraining gear, “e” represents the clearance between an outer periphery of said urging member and an inner periphery of said spring receiver, and “f” represents the length of engagement between said urging member and said spring receiver.
 10. A magnetic tape cartridge comprising: a cartridge case where a single reel with magnetic tape wound thereon is rotatably housed; and reel-rotation restraining means which, when not used, goes to a locked state to restrict rotation of said reel and, when used, goes from said locked state to an unlocked state to allow said rotation; said reel-rotation restraining means having a restraining member for restricting rotation of said reel by moving toward or away from said reel, an urging member for urging said restraining member in a restraining direction, and an unlocking member for moving said restraining member in an unlocking direction, by rotating integrally with said reel and moving according to a chucking operation of rotation means of a drive unit; wherein said restraining member has a restraining gear which meshes with a locking tooth portion formed in said reel to restrain rotation of said reel; and a tooth of said restraining gear has two inclined faces which have an apex angle and interior angles, said apex angle being between an apex angle of the locking tooth portion of said reel and 90 degrees, and said interior angles being 30 degrees or greater with respect to a vertical line and also being approximately the same.
 11. The magnetic tape cartridge as set forth in claim 10, wherein said locking tooth portion and the tooth of said restraining gear are formed from synthetic resin material. 